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Vkbikes posted a topic in Old Gen.: 80's GL/DL/XT/Loyales...Hello, I just installed a VDO vac/Boost combo gauge in my gl10 turbo. Measured at the plenum (after Throttle Body): -20 inHg at idle (looks good) ~4psi at wide open. (low?) Measured at turbo outlet 0 inHG at idle ~8psi at wide open. So i have two questions, but they relate to one another. I get with the throttle plate closed (idle) i shouldn't see almost any vacuum at the turbo outlet. However how come i don't see vacuum when i press on the accel and i only see when boost starts to build? Shouldn't the (negative) pressure wave travel down the intake? Or is the flow rate too low to see a difference? That would explain the lower boost numbers, however what number is more accurate when determining performance; why do most boost gauges measure from the wastegate if those numbers don't take vacuum into account? And which is more accurate? Does my engine see "8 psi of boost" (the actual boost the turbo puts out) or "4 psi of boost" (the actual amount of boost minus the residual vacuum) Or is my turbo not flowing enough compressed air? Color me confused.